sigwait return 4

[Slawa Olhovchenkov]

On Wed, Aug 24, 2011 at 10:50:35PM +0300, Kostik Belousov wrote:

> On Wed, Aug 24, 2011 at 11:42:29PM +0400, Slawa Olhovchenkov wrote:
> > On Wed, Aug 24, 2011 at 10:32:02PM +0300, Kostik Belousov wrote:
> > 
> > > > > What should the system do for a delivered signal not present in the set ?
> > > > > I guess this is the case of your ktrace.
> > > > > 
> > > > > Looking at the SUSv4, I see no mention of the situation, but in Oracle
> > > > > SunOS 5.10 man page for sigwait(2), it is said explicitely
> > > > > EINTR The wait was interrupted by an unblocked, caught signal.
> > > > 
> > > > I don't think you right in this case.
> > > > This is kas-milter and in this thread (this is multi-thread
> > > > application) kas-milter wait for USR2 for reload config.
> > > > 
> > > > System return from sigwait only on USR2, but not each return w/
> > > > non-zero return code.
> > > > 
> > > > On freebsd7 this application don't complain about sigwait's return value.
> > > 
> > > Could it be that some other thread has the signal unblocked ?
> > > (You can verify this with procstat -j).
> > > 
> > > Can you write the self-contained test case that demonstrates the behaviour ?
> > 
> > This is closed-source software.
> How is this statement related to the creation of the standalone test case ?
> 
> > # procstat -j
> >   PID    TID COMM             SIG     FLAGS
> >  1395 100199 kas-milter       USR2     --
> >  1395 100232 kas-milter       USR2     --
> 
> Both threads have the signal not blocked. This is not definitive,
> since signal must be blocked during the call to sigwait(2). Note that
> the SUSv4 says that "The signals defined by set shall have been
> blocked at the time of the call to sigwait(); otherwise, the behavior is
> undefined."

I see some strange in debug:

# kdump -H -f /ktrace.out | grep sigw
  1396 100228 kas-milter CALL  sigwait(0xffdfdf80,0xffdfdf7c)

# ktrdump | grep sigw
   738 syscall: td=0xffffff002549d900 pid 1396 sigwait (0xffdfdf80, 0xffdfdf7c, 0xffffff8117827bf0)
   666 syscall: td=0xffffff000c3d9900 pid 1286 sigwait (0x7fffffbfef70, 0x7fffffbfef8c, 0)
   660 syscall: td=0xffffff00251ed900 pid 1277 sigwait (0x7ffffddeff70, 0x7ffffddeff8c, 0)
    51 syscall: td=0xffffff0004ac5000 pid 787 sigwait (0x7fffffffebb0, 0x7fffffffebdc, 0)

now I see 3'th non-zero argument from pid 1396.